 |
|
 |
|
All programs, specifically those used in safety relevant applications, should have a strong modularity and must be written, so they can be easily understood. This is specifically true for programs written in assembly language and very important, because the assembler translation program (the "assembler") does no logical or syntactical check of the program. Such checks are typically provided, when using high level language compilers.
The general guidelines are:
1. One subroutine should not exceed the length of about 50 statement, which is one printed page.
2. Even if the length of the program increases, not all possible instructions should be used to help the ease of understanding.
3. No tricks !
Benefits:
* clear programs
* reduced time for program review
* changes can be made locally without effecting the whole program
Suggested Minimum Guidelines:
1. Date, Author, Version of the program first entry
2. Only one entry at the beginning and one exit at the end per subroutine
3. Subroutines are called per standard "call" instruction
4. Build macros for often used constructs, and only for these
5. "push" registers at the beginning, "pop" at the end of a subroutine
6. If ever possible, no stack manipulations
7. First statement should be the label and a short comment only
8. Fill unused program space with "Reset" instructions
9. If possible do not use "org" instructions
10. Do not use self modifying or dynamic generated code
11. Rebuild constructs from high level languages (while, repeat, case, etc.)
12. Parameter passing should be consistent for all parts of the source code. No mix of different methods
Example:
ROM_TEST ; Checks Rom by simple add
;+
; ROM_TEST, E. Pofahl, 12-Mar-86
; Version 2.1, 14-Apr-86, Fritz Mueller, Programm simplified
; -
Push_Reg ; Makro to save BC, DE, HL
LD HL, ROM_TEST ; first cell
LD B, ROM_TEST_Ende-ROM_TEST ; program length
LD A, 0
Loop: ADD A, (HL) ; add cells
INC HL ; inc pointer
DJNZ Loop ;
CP ROM_TEST_Summe
JR Z, Ex ; Yes, exit loop
LD (Fehler), A ; Set Errornumber
LD A, ROM_Fehler
EX:
Pop_Reg ; Makro to restore BC, DE, HL
ROM_TEST_End:
RET
Parts of the documentation can be included in the source code, if
clearly marked and extractable, e.g. with start with ";+" and end with
";-" (see example)
|
|
|
 |
|
 |
Produkte und Systeme